1. Field of the Invention
This invention relates generally to a pickup cartridge, and more particularly to an improved pickup cartridge provided with a novel magnetic circuit.
2. Description of the Prior Art
A prior art pickup cartridge, especially a so-called moving magnet type pickup cartridge includes such a magnetic circuit which generally consists of four pole pieces arranged in relation of 90.degree. with one another to form an air gap, yokes each being bent at right angles from each of the pole pieces, a coil wound on each of the yokes, and a short core for magnetically short-circuiting the ends of each of the yokes after the respective coils are wound on the respective yokes. Accordingly, it is necessary for the prior art pickup cartridge to provide means for integrally forming the pole pieces of different angles and yokes, and also to provide the short cores separately, which results in that the construction and assembly of the pickup cartridge becomes complicated.
Further, since the magnetic circuit or path of the prior pickup cartridge is formed of the pole pieces, yokes and short cores, the magnetic circuit or path becomes long and has high magnetic resistance or reluctance. Thus, such a defect appears that the output characteristics can not be selected so large.
In the art there has been also proposed such a picku cartridge, in which several thin core plates or layers each having no joint and being of approximately U-shape, are laminated and detecting coils are directly or with no bobbins wound on the leg portions of the laminated core. According to the above pickup cartridge having the above magnetic circuit, it is ascertained that the high frequency characteristics and so on upon a record reproduction become good.
With such the above kind of pickup cartridges, when the coil is wound on the core, at first the core is griped by a chuck or the like to determine its rotation center, while a coil wire fed from a coil wire drum provided on a part of a coil winding machine is introduced to a nozzle disposed between the leg portions of the core. Then, while the nozzle is moved, one leg portion of the core, generally the core is rotated to directly wind the coil wire from the nozzle on the one leg portion of the core as a detecting coil. By the similar operation, on the other leg portion of the core, a detecting coil is also wound.
According to the above core, since the coils are directly wound on both leg portions of the core, there occur such a defect that the insulating coating layer of the coil wire is easily damaged by the tip end of the nozzle, sharpe edges of the leg portions or the like during the winding process, and also that the insulating layer on the leg portions are frequently damaged. As a result, there occurs frequently such a trouble that the short-circuiting is caused between the detecting coil and the core, and between the wires of the coil. By the above defects, the yield of the worked magnetic circuit is lowered and the working property of the winding process per se is poor.